JP2544229B2 - Pervaporation separation method of organic compound mixture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a heat-resistant asymmetric separation membrane containing a mixture of organic compounds such as an organic solvent solution in which an organic compound is dissolved, which is made of a specific aromatic polyimide. The at least one organic compound in the organic compound mixture liquid is brought into direct contact with and is selectively permeated and permeated through the asymmetric separation membrane to selectively permeate through the asymmetric separation membrane. The present invention relates to a pervaporation separation method (pervaporation method) of an organic compound mixed liquid for separating and recovering an organic compound as vapor.

[Description of Prior Art]

Conventionally, a distillation method has been known as a method of separating an organic compound mixed liquid into each component. However, it has been extremely difficult to separate an azeotropic mixture, a near-boiling mixture, or an organic compound that easily undergoes a chemical change by heat by the distillation method.

In order to solve these problems, a method of separating using a separation membrane has been studied. In a method of concentrating and separating an organic aqueous solution using a separation membrane, for the concentration of some low-concentration organic matter aqueous solutions, contact the organic aqueous solution with the separation membrane and select a specific liquid component by the difference in osmotic pressure. Reverse osmosis has been used to selectively permeate. However, the reverse osmosis method cannot be applied to a high-concentration organic matter aqueous solution having a high osmotic pressure because it is necessary to apply a pressure equal to or higher than the osmotic pressure of the separated liquid. Therefore, the concentration range of the separable organic matter aqueous solution is limited. is there.

Recently, a pervaporation method (pervaporation method) is used as a method for separating an organic compound mixture that is different from the conventional separation method.
As a new separation method using a separation membrane, it is getting attention.
This pervaporation method, one side of the separation membrane having selective permeability (supply side), the organic compound mixed liquid to be separated is supplied in a liquid state, and directly contact with the supply side of the separation membrane,
The other side (permeation side) of the separation membrane is placed in a vacuum or reduced pressure state, and as a result, the substance selectively permeating from the supply side to the permeation side of the separation membrane is taken out in a gaseous state to concentrate the organic compound mixture liquid. , A method of separating each organic compound.

Many proposals have been made for the pervaporation method described above.

For example, a benzene-cyclohexane mixed solution, or
Regarding the separation of a benzene-hexane mixed solution, see
52-111888 discloses a separation method using an ionomer polymer membrane, and JP-A-59-30441 discloses a separation method using a polyamide membrane.

However, in the known separation method of an organic compound mixed solution, the separation membrane used in the pervaporation method has a low permeation rate or selectively permeates at least one organic compound in the organic compound mixed solution. Has a problem that it has only selective separation that cannot be sufficiently, or the separation membrane used in the known pervaporation method, heat resistance, or
The solvent resistance was not sufficient, and it was extremely difficult to industrially perform separation of various organic compound mixed liquids by pervaporation for a long time.

[Problems to be solved]

An object of the present invention is to efficiently and selectively remove at least one organic compound from an organic compound mixed solution in the pervaporation method of an organic compound mixed solution using an asymmetric separation membrane without the drawbacks of known pervaporation methods. It is an object of the present invention to provide a pervaporative separation method which can be separated by the pervaporative method and can be industrially used for a long period of time.

[Means for solving problems]

The present invention (However, in the general formula I, A represents a divalent residue excluding the two amino groups of the aromatic diamine compound.) A heat-resistant aromatic polyimide having a repeating unit of 40 mol% or more. The organic compound mixture is brought into direct contact with one surface of the asymmetric separation membrane so that at least one organic compound in the organic compound mixture is selectively permeated and permeated through the asymmetric separation membrane. The method for permeation vaporization separation of an organic compound mixed liquid, characterized in that the organic compound permeated through the asymmetric separation membrane is separated as vapor.

Hereinafter, each requirement of the present invention will be described in more detail.

The aromatic polyimide used for forming the asymmetric separation membrane used in the pervaporation separation method of the present invention has the general formula (I).
Containing 40 mol% or more, particularly 45 mol% or more of the repeating unit represented by [However, in the general formula II, A has the same meaning as A in the general formula (I)], and a soluble aromatic polyimide is preferable.

The soluble aromatic polyimide containing 40 mol% or more of the repeating unit represented by the general formula (I) has the general formula Containing 40 mol% or more, especially 45 mol% or more, of diphenylhexafluoropropane-based tetracarboxylic acid dianhydride or its derivative (lower alcohol esterified product thereof) shown in An aromatic tetracarboxylic acid component which is a biphenyl tetracarboxylic dianhydride or a derivative thereof represented by
Mainly aromatic diamine compounds having benzene rings (80 mol% or more relative to the total aromatic diamine component, especially
90 mol% or more) with an aromatic diamine component
It is preferably a soluble aromatic polyimide obtained by imidization.

The aromatic polyimide, for example, an aromatic tetracarboxylic acid component and an aromatic diamine component are uniformly dissolved in a phenolic organic solvent, the solution is about 150 ~ 2
It is produced by heating both components in the above solution by weight and imidization by heating to a high temperature of 50 ° C. or by reacting at a low temperature of about 10 to 100 ° C. in the presence of an imidizing agent. You can

As the diphenylhexafluoropropane-based tetracarboxylic acid dianhydride represented by the general formula (III), for example, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride can be preferably mentioned. Further, the biphenyltetracarboxylic dianhydride represented by the general formula (IV) may be 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,3 ′, 4 ′. -Biphenyl tetracarboxylic dianhydride can be mentioned suitably.

In the present invention, examples of the aromatic diamine compound having 2 to 4 benzene rings include diaminodiphenyl ethers, diaminodiphenylthioethers, diaminodiphenylsulfones, diaminodiphenylmethanes, diaminodiphenylpropanes, diaminodibenzothiophenes and diamino. "Aromatic diamine compound having two benzene rings" such as thioxanthenes, "Aromatic diamine compound having three benzene rings" such as di (aminophenoxy) benzenes, di (aminophenyl) benzenes, di [ "Aromatic diamine compounds having four benzene rings" such as (aminophenoxy) phenyl] alkanes, di [aminophenoxy) phenyl] sulfones, and di (aminophenoxy) biphenyls can be mentioned.

As typical examples of the aromatic diamine compound having two benzene rings, diaminodiphenyl ethers such as 4,4'-diaminodiphenyl ether and 3,4'-diaminodiphenyl ether, 4,4'-diaminophenylmethane, 3,4 Diaminodiphenylmethanes such as ′ -diaminodiphenylmethane, 4,4′-diamino- (2,2-diphenylpropane), diaminodiphenylpropanes such as 3,4′-diamino- (2,2-diphenylpropane), 4,
4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone and other diaminodiphenyl sulfones, 3,7-diaminodibenzothiophene, 3,7-diaminodibenzothiophene-5,5-dioxide, 2,8-dimethyl- 3,7-diaminobenzothiophene, 2,6-dimethyl-3,
7-diaminodibenzothiophene, 4,6-dimethyl-3,7
-Diaminodibenzothiophene, 2,8-dimethyl-3,7-
Diaminodibenzothiophene-5,5-dioxide, 2,6-
Dimethyl-3,7-diaminodibenzothiophene, -5,5-
Dioxide, 4,6-dimethyl-3,7-diaminodibenzothiophene, -5,5-dioxide, 2,8-diethyl-3,7-
Diaminodibenzothiophene, 2,6-diethyl-3,7-diaminodibenzothiophene, 4,6-diethyl-3,7-diaminodibenzothiophene, 2,8-diethyl, -3,7-diaminodibenzothiophene-5,5 -Dioxide, 2,6-diethyl-3,7-diaminodibenzothiophene-5,5-dioxide, diaminodibenzothiophenes such as 4,6-diethyl-3,7-diaminodibenzothiophene-5,5-dioxide, 3 , 7-Diaminothioxanthene, 3,7-diaminothioxanthene-5,5-dioxide, 2,8-dimethyl-3,
7-diaminothioxanthene, 2,6-dimethyl-3,7-diaminothioxanthene, 4,6-dimethyl-3,7-diaminothioxanthene, 2,8-dimethyl-3,7-diaminothioxanthene-5, 5-dioxide, 2,6-dimethyl-3,7-
Examples include diaminothioxanthene-5,5-dioxide, diaminothioxanthenes such as 4,6-dimethyl-3,7-diaminothioxanthene-5,5-dioxide, and diaminodiphenyls such as o-anisidine. it can.

The aromatic tetracarboxylic acid component in the above-mentioned method for producing an aromatic polyimide is, in addition to diphenylhexafluoropropane-based tetracarboxylic acids, for example, pyromellitic acid or an acid dianhydride thereof, 3,3 ′, 4,4 ′. -Diphenyl ether tetracarboxylic acid or its acid dianhydride, 3,3 ',
Although 4,4'-benzophenone tetracarboxylic acid or its acid dianhydride can be used in combination, pyromellitic acid is preferably 25 mol% or less, particularly preferably 20 mol% or less, based on all acid components. .

In the above method for producing an aromatic polyimide, m-with an aromatic diamine compound having 2 to 4 benzene rings.
A small proportion of phenylenediamines such as phenylenediamine and p-phenylenediamine (preferably 15 mol%)
The following, particularly 10 mol% or less) may be used in combination, and diaminobenzoic acid such as 3,5-diaminobenzoic acid and 2,6-diaminobenzoic acid, or alkylbenzenediamines are small. It may be used in combination at a ratio (preferably 30 mol% or less, particularly 25 mol% or less).

The above-mentioned asymmetric separation membrane made of the aromatic polyimide used in the present invention uses a phenol-based solvent solution of the aromatic polyimide to form a thin film (flat membrane,
Hollow fiber) is formed by a casting method, an extrusion method, or the like,
Then, the thin film can be manufactured by a wet film forming method in which the thin film is brought into contact with a relatively low-temperature coagulating liquid to solidify the thin film to form a flat membrane-shaped or hollow fiber-shaped asymmetric separation membrane. It can be produced by a conventionally known film forming method as described in JP-A-56-21602 and JP-A-56-157435.

In the above-mentioned method for producing an asymmetric separation membrane, the asymmetric separation membrane produced by the wet membrane production method is a suitable organic solvent (for example, lower alcohols such as methanol, ethanol, propanol, butanol, and n-hexane). , N
-Heptane, octane, cyclohexane and other aliphatic or alicyclic hydrocarbon solvents, etc.), and further after sufficiently dried, further under a gas atmosphere of nitrogen, air, etc., about 150 ~ 400 ℃, especially It is suitable to perform heat treatment or aging treatment for about 1 second to 20 hours at a temperature of 180 to 350 ° C. When the heat treatment is sufficiently carried out at a high temperature of 250 ° C. or higher, the aromatic polyimide forming the asymmetric separation membrane is partially thermally crosslinked, and is insolubilized or swelled particularly in a solvent. It is preferable because it does not occur and chemical resistance and durability are improved.

The asymmetric separation membrane used in this invention has a thickness of about 0.00
Homogeneous layer (dense layer) of 1 to 5 μm and thickness of 10 to 2000 μm
a flat membrane-like separation membrane having a porous layer of m
It may be a hollow fiber separation membrane or the like.

The asymmetric separation membrane used in the present invention has a permeation amount Q of the permeating organic compound of about 0.1 kg / m ² · Hr or more, particularly about
It is about 0.2 to 5 kg / m ² · Hr, and it is preferable that the separation performance (separation coefficient α described later) between the permeated organic compound and the non-permeated organic compound is 5 or more, particularly 10 to 10000. .

The pervaporative separation method of the present invention comprises: (a) supplying an organic compound mixed liquid to a separation membrane module containing the asymmetric separation membrane (flat membrane shape, hollow fiber shape) made of the aromatic polyimide described above, and The organic compound mixture is brought into direct contact with the supply side of the asymmetric separation membrane in the separation membrane module, and (b) the permeate side of the asymmetric separation membrane is supplied with a carrier gas (sweep gas) if necessary. While flowing, or by connecting to a decompression pump or the like installed outside the separation membrane module to be in a decompressed state, from the supplied organic compound mixed liquid, through the asymmetric separation membrane, at least one organic compound. The compound is selectively permeated and permeated to be vaporized and separated (c) Finally, from the non-permeate side (supply side) of the asymmetric separation membrane to the outside of the separation membrane module, the separation membrane The concentrated residual organic compound solution that did not permeate was taken out and recovered, and at the same time, the permeation vapor (permeate) of the organic compound that permeated the separation membrane from the permeation side of the asymmetric separation membrane to the outside of the separation membrane module. Is taken out, and if necessary, the permeated vapor (permeate) is cooled and condensed to be recovered.

In the present invention, the organic compound mixture supplied to the separation membrane module is about 0 to 120 ° C, particularly preferably 20 to 100 ° C.
It is preferable that the temperature is moderate.

In the separation method of the present invention, the pressure applied to the separation method is usually a pressure on the permeate side of the separation membrane that is lower than the pressure on the feed side, and the pressure on the feed side is atmospheric pressure to 60 kg / cm ² , preferably The atmospheric pressure is preferably set to 30 kg / cm ² .

The permeate side of the asymmetric separation membrane in the separation membrane module, when performing pervaporative separation of the organic compound mixture, may be swept gas, or may be under reduced pressure,
The reduced pressure may be lower than atmospheric pressure, particularly preferably about 200 torr or less, and more preferably 100 torr or less.

The organic compound mixed liquid to which the pervaporation method of the organic compound mixed liquid in the present invention can be applied is an organic compound that does not substantially dissolve the aromatic polyimide forming the asymmetric separation membrane. Is preferable, and, for example, a mixture of organic compounds that cannot be separated by a normal distillation method because each organic compound has an azeotropic point, and the boiling points of the organic compounds are close to each other. It is especially effective in the case of a mixture of organic compounds which is very difficult to separate by distillation.

Further, all of the organic compound mixed liquids may be uniformly dissolved in each other, or some of them may exceed the solubility and be separated to be in a suspended state. However, the mixed liquid containing the organic compound needs to be liquid under the conditions of temperature and pressure when performing pervaporation separation in the mixed state.

Examples of the mixed liquid of an organic compound having an azeotropic point include benzene / cyclohexane, benzene / normal hexane, benzene / methanol, ethanol / cyclohexane, butanol / cyclohexane, and ethanol / benzene.

Further, as the organic compound mixture liquid having a boiling point difference of about 20 ° C. or less, particularly 10 ° C. or less and boiling points close to each other,
Examples thereof include butadiene / butenes, butadiene / butanes, and normal butene-1 / isobutene.

The above-mentioned mixed liquid of organic compounds can be applied not only to the above-described two-component mixed liquid, but also to a three-component or more multi-component mixed liquid.

In the pervaporation separation method of the present invention, the composition ratio of the above-mentioned organic compound mixed liquid is not particularly limited, and a mixed liquid of organic compounds in an arbitrary ratio can be separated or concentrated.

The structure, form, etc. of the separation membrane module are not particularly limited, and examples thereof include, but are not particularly limited to, plate-and-frame type modules, spiral type modules, and hollow fiber membrane type modules. It is preferable.

〔Example〕

Examples of the pervaporative separation method of the present invention will be shown below to explain the present invention in more detail.

In the examples, the permeation amount Q and the separation coefficient α were measured by cooling and condensing the vaporized component that permeated the membrane, collecting the weight, measuring the weight of the vaporized component, adding the internal standard solution to the condensate, and measuring the TCD.
-The weight ratio of the organic compounds X and Y was measured by gas chromatography and calculated by the following formula.

In the reference example, the abbreviations of the compounds used for the aromatic tetracarboxylic acid component and the aromatic diamine component are shown below.

[Aromatic tetracarboxylic acid component]

6-FDA; 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride s-BPDA; 3.3 ', 4,4'-biphenyltetracarboxylic dianhydride PMDA; pyromellitic dianhydride Compound [aromatic diamine compound] TSN; 2,8-dimethyl 3,7-diaminodibenzothiophene-
5,5-dioxide, 2,6-dimethyl-3,7-diaminodibenzothiophene-5,5-dioxide, 4,6-dimethyl-3,
Isomeric mixture of 7-diaminodibenzothiophene-5,5-dioxide DADE; 4,4'-diaminodiphenyl ether DADM; 4,4'-diaminodiphenylmethane Reference Examples 1 to 4 Using an approximately equimolar amount of the diamine component, polymerization and imidization were carried out in an organic polar solvent of parachlorophenol at a polymerization temperature and a polymerization time shown in Table 1 to produce an aromatic polyimide solution.

Table 1 shows the polymer concentration and the solution viscosity (rotational viscosity at 100 ° C .; poise) of each aromatic polyimide solution produced as described above.

Using the aromatic polyimide solution obtained as described above, a wet film-forming method using a coagulating liquid (ethanol aqueous solution) having a composition shown in Table 1 and a hollow fiber take-off speed of 10 m / min. After forming a hollow fiber membrane with, washed with alcohol and aliphatic hydrocarbon, dried and heat-treated for 30 minutes at the heat treatment temperature shown in Table 1, the shape shown in Table 1 (inner diameter of hollow fiber and Asymmetric hollow fiber separation membranes made of aromatic polyimide having a film thickness) were produced.

Examples 1 to 5 Four 7.5 cm long asymmetric hollow fiber separation membranes produced in each reference example are bundled to form a yarn bundle, and one end of the yarn bundle is sealed with an epoxy resin, A hollow fiber bundle element is prepared, and the hollow fiber bundle element is internally provided in a container having an inlet for supplying an organic compound mixed liquid, an outlet for the non-permeate and an outlet for the permeate, and a separation membrane module. Was manufactured.

The organic compound mixture having the composition and temperature shown in Table 2 was supplied to the separation membrane module, and the inside of the hollow fiber of the hollow fiber element in the separation membrane module was pervaporated under a reduced pressure of 3 Torr or less, The permeate vapor was cooled and recovered.

Table 2 shows the permeation amount Q in pervaporation and the separation coefficient α of each organic compound.

[Operation and effect of the present invention] The separation method of the present invention is a separation method relating to the pervaporation method using an asymmetric separation membrane made of a specific aromatic polyimide, so that it is possible to separate and concentrate a mixed solution of various organic compounds. Can be used, and can be used for a wide range of concentrations of organic compound mixtures, yet with sufficient heat resistance,
It has water resistance, solvent resistance and durability, and furthermore,
Since a specific polyimide asymmetric membrane having high separation performance is used, separation by a stable pervaporation method can be performed for a long time.

Claims (1)

(57) [Claims] 1. A general formula (However, in the general formula I, A represents a divalent residue excluding the two amino groups of the aromatic diamine compound.) Heat resistance comprising an aromatic polyimide having 40 mol% or more of the repeating unit represented by By directly contacting the organic compound mixture with one surface of the asymmetric separation membrane of, at least one organic compound in the organic compound mixture is selectively permeated and permeated through the asymmetric separation membrane. A method for pervaporative separation of an organic compound mixture, wherein the organic compound that has passed through the asymmetric separation membrane is separated as vapor.